1. Field of the Invention
This invention relates to the field of systems for moving and stacking paper or plastic bags weighing between 20 and 200 pounds that contain granular material such as cement, sand, or food stuffs, in preparation for storage or shipment of the packaged merchandise.
2. Prior Art
A bag palletizer loads layers of filled bags onto a pallet in a predetermined pattern. An interlocking relationship of alternating layers of alternating rows and columns of bags is frequently required.
A bag palletizing system is typically a sequential machine operating under the control of a computer or sequential sequencer. The system conventionally has a conveyor feed system for receiving filled bags from a source such as another conveyor. Guides feed the bags onto the moving conveyor of the palletizing apparatus. The guides initially position and locate the bags on the palletizing conveyor to move the bags along a predetermined course to a discharge point onto the pallet.
The pallet is moved after receiving each bag, from the palletizing conveyor to the next position for receiving the next bag. Movement of the pallet is also under spacial computer sequential control with motion of the pallet being controlled in an X, Y and Z coordinate system to accommodate the size of the bag, the speed of the conveyor, the texture and density of the material in the bags, the bag material and finally the desired pattern to be formed by the bags as they leave the conveyor and are deposited on the pallet.
Bag palletizing systems are designed to assist in stacking bags on a pallet with minimum assistance from loading personal. The bags are always positioned on the pallet to form a rectangle; therefore, precise orientation of the bags to align the longitudinal axis of the bag on a precise track parallel to the direction of motion of the palletizer conveyor or along an axis transverse to the direction of motion of the palletizer conveyor is required to reduce the assistance required from the bag stacking personnel.
Precise rotation of the bag while the bag is moving on the palletizer conveyor is critical to precise stacking and to minimizing the possibility of damage to the moving bag. Systems of early design used manually operated guides or manual force to rotate the bags to a correct orientation as they moved along the bag stacker conveyor. Poor accuracy and bag damage frequently resulted from manually controlled bag turning means.
A post was used as a bag turner on early bag stacking systems. The post was positioned off the center path of the bag on the palletizing conveyor. As the bag reached the post-type, a corner of the bag would be stopped by the post allowing the bag to pivot on the moving conveyor surface as the conveyor moved the bag past the post. The post-type bag turning apparatus had a speed limitation. The speed of the conveyor had to be reduced to prevent damage to the bags as they impacted the post prior to rotation. The post-type bag turner also proved to be unsatisfactory for use with plastic bags due to its tendency to damage plastic bags even at relatively low speeds.
A pop-up turntable has also been used in connection with palletizing conveyors to turn bags. As the bags reached the turntable, the turntable would pop up under the bag, to support the bag and to rotate the bag to position the longitudinal axis of the bag to be transverse with the motion of the palletizing conveyor. Pop-up turntable bag turners proved to be more complex than the post turners. The pop-up bag turners had many more parts and parts that were much more expensive to fabricate.
The post type had a maximum speed limit of approximately 30 bags per minute. The pop-up bag turners had a maximum speed limit of approximately 20 bags per minute without damaging the paper bags. The bag turner has proved to be the factor that most significantly limits the speed of bag palletizing systems.